The invention concerns a grinding device with a grinding stone for sharpening at least on knife of a chopper arrangement, and more specifically relates to a control for a movement arrangement for moving the grinding stone.
During the operation of a forage harvester, the knives fastened to the chopper drum wear over time. It is possible that individual knives wear to differing degrees. While the knives at a given zone around the circumference of the chopper drum, as a rule, wear approximately at a uniform rate, the wear across the width of the chopper drum can differ considerably. Therefore, the diameter of the enveloping circles described by the cutting edges of the knives can vary in the axial direction of the shaft of the chopper drum. A cylindrical or slightly concave shape is desirable, in order to simplify an automatic repositioning of the shearbar or to make that possible, depending on the repositioning system. A parallel and exact repositioning of the shearbar to the circumference of the chopper drum is indispensable for an effective chopping process.
One attempt at automating the sharpening of chopper drum knives, so as to result in a cylindrical drum profile instead of undesirable barrel or hour glass shaped drum profiles, and for repositioning the shearbar is disclosed in U.S. Pat. No. 4,843,767, granted on Jul. 4, 1989 to Johnson. This patent discloses a grinding stone moving arrangement, including a guide rail and stone carrier mounted for movement as a unit toward and away from the chopper drum by a first electric motor, with the stone carrier being swept across the chopper drum by operation of a second electric motor. These electric motors, and an additional pair for repositioning the shear bar, are controlled by a microprocessor including a programmable memory and to which signals from knock sensors mounted at the shearbar are sent for use in determining in-feed and sweep movements of the grinding stone as well as for use in determining how far to reposition the shearbar. The microprocessor also receives information by which the operator is informed of the instant lateral position of the grinding stone by the sequential lighting of a series of LEDs during its sweep movements. However, with this and other known grinding devices, there is no provision for equalizing the deviations in the diameter of the chopper drum along the length of the drum during the grinding process without manually measuring the chopper drum and subsequently grinding away a sufficient amount.
U.S. Pat. No. 5,103,622, granted to Hall et al. on Apr. 14, 1992 discloses a grinding arrangement wherein the grinding stone is mounted to a carrier that is guided for moving adjacent the cylinder described by the rotating knives of the chopper drum. The grinding stone is mounted to a holder formed in part by a screw having a ratchet wheel at its upper end which engages a trip member, during each cycle of the carrier across the width of the chopper drum, so as to index the screw and move the grinding stone a small increment towards the chopper drum. The guide rail for guiding the carrier is shaped so as to result in the chopper drum being sharpened to a more true cylindrical shape.
DE 40 23 114 A describes a process to determine the sharpness of chopper knives, in which the sharpness of the chopper knives is measured by a magnetic sensor attached to the grinding device. By moving the grinding device with the sensor attached thereto transverse to the chopper drum, the sharpness of the chopper knives can be measured across the width of the chopper drum. The values measured by means of the sensor are used to inform the operator of the forage harvester when the chopper knives must be ground.
DE 199 03 153 C proposes that the wear condition of individual chopper knives be determined by the measurement of the load on the shearbar opposite to the direction of flow of the crop and transverse to the direction of flow of the crop. In case the measured wear condition indicates dull knives, the operator is given a corresponding information, or the flow of the crop is automatically stopped, or the shearbar is repositioned, or a grinding process is initiated.
The problem underlying the invention is seen in the need to make available an improved grinding device which results in the sharpened knives having a desired spacing from a fixed shearbar or counter knife for good chopping results.
According to the present invention there is provided an improved grinding device.
An object of the invention is to provide a grinding device which takes into account irregularities in the shape of the circumference of a chopping drum along its length or rotational axis.
A more specific object of the invention is to provide a control for a grinding device which includes a memory for storing a value representing a target shape of the profile of the chopping drum and for retrieving signals from a measuring arrangement of the actual shape of the chopping drum and comparing them with the target shape and controlling the grinding device in view of this comparison so as to shape the chopping drum profile to at least approximate that of the target shape.
These and other objects will become apparent from a reading of the ensuing description together with the appended drawing.